The discovery of a Higgs boson [1]}, [2]}, [3]} with a mass near 125 [4]}, [5]} provided new motivation to search for an extended Higgs sector at the CERN LHC. These searches are focused not only on additional Higgs bosons at high mass, but also on possible light states below 125, which may have eluded earlier detection. Light (pseudo)scalar bosons are predicted in a number of beyond the standard model (SM) theories, e.g., in two Higgs doublet models (2HDM) [6]} and next-to-minimal supersymmetric SM (NMSSM) [7]}. Despite an extensive program of searches for such resonances by the CERN LEP experiments [8]}, [9]}, [10]}, [11]}, [12]}, and by the ATLAS [13]}, [14]}, [15]}, [16]}, [17]}, [18]}, [19]}, CMS [20]}, [21]}, [22]}, [23]}, [24]}, [25]}, [26]}, [27]}, and LHCb [28]} Collaborations, the present experimental limits on the product of production cross sections and branching fractions do not yet exclude the existence of such particles [29]}.
